Not Applicable.
The present invention relates generally to medical implements, and more particularly to a medical implement that employs a mechanically supported expandable membrane as part of the implement.
It is well known to perform an angioplasty procedure to open an arterial vessel that, for example, is occluded due to arteriosclerosis. Typically, a balloon catheter is inserted into a patient""s arterial network and manipulated to the occluded region of the vessel which is often proximate the heart. The balloon portion of the catheter is inflated so as to compress the arterial plaque against the vessel walls. The luminal area of the vessel is thereby increased, allowing more blood to flow through the vessel.
While the angioplasty procedure may initially be successful, a significant percentage of patients experience restenosis of the treated area. That is, the opened region of the vessel gradually recloses in a relatively short amount of time, such as about six months. Although the exact mechanism is not understood, restenosis is generally believed to involve platelet aggregation, thrombus formation, and smooth cell migration and proliferation, either singly or in combination. However it occurs, restenosis ultimately negates the benefits achieved by the angioplasty procedure.
In order to prevent mechanical recoil of the vessel wall following angioplasty, as well as to mitigate the effects of restenosis, a stent may be implanted in the opened region of the vessel after the angioplasty procedure. As known to one of ordinary skill in the art, a typical stent has a generally cylindrical shape to conform to the vessel and can be formed from a wire mesh. However, stents may irritate the vessel wall. Further, in some patients stents are believed to be the cause of rapid tissue growth, or intimal hyperplasia, through openings in the stent walls.
Some prior art devices and methods have called for the use of cooling treatment to prevent restenosis. For example, U.S. Pat. No. 5,417,653 briefly discusses a method of inhibiting restenosis by reducing the temperature of tissue at a treatment site by infusion of a fluid such as n-saline. However, fluid infusion as a treatment method may be inaccurate in targeting desired tissue and may introduce unwanted fluids or pathogens into a patient.
It would, therefore, be desirable to provide a device capable of treating a vessel region to prevent restenosis without the disadvantages highlighted above.
The present invention provides a medical implement comprising an expandable membrane with an element disposed within a lumen formed by the membrane. One embodiment of such an implement may be a mechanically supported balloon used as part of a catheter. In yet another embodiment, a mechanically supported balloon is incorporated as part of a cryogenic catheter that delivers cryogenic energy to minimize restenosis of a dilated region of a treated blood vessel. Cryogenic fluid is delivered to the expanded balloon and thereby cools the tissue in contact with an outer side of the balloon. Mechanical support for the balloon may, for example, be provided by a helical shape memory coil or a series of shape memory sections that deform against an inner side of the balloon, thus inflating the balloon. A variety of alternate mechanical support schemes may be employed to reach a similar result.